As a production method of polymer obtained by reacting an aromatic polyester and a lactone, a method comprising reacting a crystalline aromatic polyester and a lactone (JP-B-48-4116), a method comprising reacting a crystalline aromatic polyester and a lactone and reacting the obtained initial block copolymer and a polyfunctional acylating agent to allow extension of its chain (JP-B-48-4115), a method comprising polymerizing a lactone in a solid state in the presence of a crystalline aromatic polyester (JP-B-52-49037) and the like are known.
The polymers obtained by these methods are thermoplastic and have superior rubber like elasticity. However, they have insufficient heat resistance and when exposed to high temperature for a long time, the strength and elongation reduce strikingly. In addition, these polymers have insufficient water resistance and are susceptible to hydrolysis in the presence of water. For these reasons, it is difficult to put the compositions containing these polymers as they are to practice as a material for a fiber, a film, a formed product and the like.
For an improved heat resistance and an improved water resistance of the polyester block copolymer as mentioned above, a method comprising the use of an epoxy compound having one or more functional groups (JP-A-58-162654) and the like have been proposed. This method improves heat resistance and water resistance.
In addition, a method comprising adding an epoxy compound for an improved mechanical property of a polyester block copolymer obtained by copolymerization of a crystalline aromatic polyester and polyalkylene glycols such as polytetramethylene glycol may be employed.
This method, nevertheless, has problems in that a great amount of unreacted certain epoxy compounds is evaporated when the obtained compositions containing epoxy compounds are heated. When the composition is processed into a molded product and subjected to other processing steps such as coloring of resin, imparting inflammability and the like, there is a possibility that hygiene problem may occur. Moreover, generated gases may corrode cylinder and screw of an extruder, a forming machine and the like, as well as the surface of a mold, and in the field of electric equipment parts and electronic equipment parts, generated gases may corrode metallic parts, thereby causing contact failure and defective conduction. To solve these problems, the kind of epoxy compound is limited to suppress volatility during heating (JP-A-10-30053).
The addition of the aforementioned epoxy compound leads to improved heat resistance and hydrolysis of resin, and less volatility during heating, but to deal with a situation involving exposure to a harsh use environment, a stabilizer such as an antioxidant, a photostabilizer and the like is generally added. When, however, an inappropriate stabilizer is added in an inappropriate amount, the properties cannot be improved, and many problems occur such as bleeding out due to insufficient affinity for resin to impair appearance of a molded product, degraded durability and the like. In addition, an adverse influence that degrades mechanical properties and the like could be exerted. Moreover, a gel occurs during mixing of a polyester block copolymer, an epoxy compound and a stabilizer in an extruder, which in turn causes problems of clogging of a filter, impaired appearance of a molded product and the like, thereby necessitating a special stabilizer.
An object of the present invention is to provide a thermoplastic polyester elastomer composition having superior heat resistance and superior resistance to hydrolysis, which is associated with less volatility during heating, less gel or bleed-out matters.